Wood fibre based direct pressed laminated flooring usually comprises a core of a 6-12 mm fibre board, a 0.2 mm thick upper decorative surface layer of laminate and a 0.1-0.2 mm thick lower balancing layer of laminate, plastic, paper or like material.
A laminate surface generally comprise two paper sheets, a 0.1 mm thick printed decorative paper and a transparent 0.05-0.1 mm thick overlay paper applied over the decorative paper and intended to protect the decorative paper from abrasion. The print on the decorative non-transparent paper is only some 0.01 mm thick. The transparent overlay, which is made of refined fibres (e.g. α-cellulose fibres), comprises small hard and transparent aluminium oxide particles. The refined fibres are rather long, about 2-5 mm and this gives the overlay paper the required strength. In order to obtain the transparency, all natural resins that are present in the virgin wood fibres, have been removed and the aluminium oxide particles are applies as a very thin layer over the decorative paper. The surface layer of a laminate floor is characterized in that the decorative and wear properties are generally obtained with two separate layers one over the other.
The printed decorative paper and the overlay are impregnated with melamine resin and laminated to a wood fibre based core under heat and pressure.
The small aluminium oxide particles could have a size in the range of 20-100 microns. The particles could be incorporated in the surface layer in several ways. For example they could be incorporated in the pulp during the manufacturing of the overlay paper. They could also be sprinkled on the wet lacquer during impregnation procedure of the overlay or incorporated in the lacquer used for impregnation of the overlay.
The wear layer could also be produced without a cellulose overlay. In such a case melamine resin and aluminium oxide particles are applied as a lacquered layer directly on the decorative paper with similar methods as described above. Such a wear layer is generally referred to as liquid overlay.
With this production method a very wear resistant surface could be obtained and this type of surface is mainly used in laminate floorings but it could also be used in furniture components and similar applications. High quality laminate floorings have a wear resistance of 4000-6000 revolutions, which corresponds to the abrasion classes AC4 and AC5 measured with a Taber Abraser according to ISO-standard.
It is also known that the wear resistance of a lacquered wood surface could be improved considerably by incorporating aluminium oxide particles in the transparent lacquer covering the wood surface.
The most common core material used in laminate floorings is fibreboard with high density and good stability usually called HDF—High Density Fibreboard. Sometimes also MDF—Medium Density Fibreboard—is used as core. Other core materials such as particleboard are also used.
Recently new “paper free” floor types have been developed where powder technology is used to obtain a solid laminate surface comprises a substantially homogenous mix of non-processed wood fibres, binders and wear resistant particles. Such floor types are below referred to as “solid laminate” floors. The wear resistant particles are preferably aluminium oxide particles and the binders are preferably thermosetting resins such as melamine. Other suitable materials are for example silica or silicon carbide. In general all these materials are preferably applied in dry form as a mixed powder on a HDF core and cured under heat and pressure to a 0.2-1.0 mm solid (opaque) laminate layer. The solid layer in solid laminate floors provides high impact and wears resistance.
Powder technology is also used to produce floors with a surface that combines the paper technology and powder technology. Such floor types are below referred to as “wood powder laminate floors” A decorative paper is applied on a sub layer comprising wood powder and binders. The decorative paper is protected by a conventional overlay. The main advantages with such floors are that deep embossing and improved impact resistance could be obtained.
The wear resistance in wood powder laminate floors is generally not sufficient when surfaces with deep embossing is formed since the protruding parts at the surface are subject to high wear. Even some solid laminate floor with several thin layers comprising different colours suffer from a low wear resistance.
It would be a great advantage if wear resistance could be improved in a cost efficient way.
The above description of various known aspects is the applicants' characterization of such, and is not an admission that any of the above description is prior art.